Elimination of errors in absolute position encoders using m-sequences

The position of a linear or shaft-angle encoder can be obtained by reading r consecutive bits of an m-sequence of length L = 2r ¿ 1, written on a single track. The errors that occur when a read is attempted during a transition between bits are considered. It is shown how the errors can be eliminated by means of additional heads. It is found that the number of extra heads required depends on the characteristic polynomial f(x) of the m-sequence and it is shown that, by correct choice of f(x), only two extra heads are required.